1. Field of the Invention
This invention relates to compositions for removing or stripping paint, varnish, and like coatings from wood, metal, concrete and related surfaces. It particularly relates to water borne solvent compositions for removing or stripping coatings from surfaces at ambient to elevated temperatures.
2. Review of the Prior Art
Removal of protective coatings from wood and metal surfaces has long been a difficult and laborious operation involving the use of flame, heat, and/or chipping tools. Such labor has been minimized by using solvents to soften and/or lift a coating from a protected surface.
Paint and varnish removers are of two main types according to method of use: application removers and immersion removers. Application removers are usually applied by brushing or spraying and are used for small jobs or for items that cannot be immersed. Immersion removers are used as either cold or hot baths where it is practical and cost efficient to install equipment that can strip numerous items. Cold baths contain solvents such as methylene chloride, and hot baths often contain caustic soda.
Compositions for removing protective coatings have generally utilized methylene chloride and other halogenated aliphatic hydrocarbons. According to the "Kirk-Othmer Encyclopedia of Chemical Technology," Vol. 16, pp. 762-768, a typical methylene chloride remover contains 70-85% methylene chloride, 5-10% alcohol co-solvent, typically methanol, and 0-10% hydrocarbon solvent or ketones, the remainder being paraffin wax, methylcellulose, an amine, and surfactants or emulsifiers. As disclosed in this passage from "Kirk-Othmer", paint and varnish removers other than methylene chloride are also known including inexpensive solvents and blends of solvents including acetone, methyl ethyl ketone, toluene, xylene, blends of alcohol and acetates, tetrahydrofuran, dimethylformamide, and 1,1,2-trimethoxyethane.
Many patents disclose specific coating remover compositions which contain chlorinated hydrocarbon solvents. Below are listed typical examples.
U.S. Pat. No. 2,495,729 discloses use of a film-forming base material, such as cellulose esters to increase the viscosity and form a protective film which enables the solvent and softening agents of a coatings remover to be confined within the film to exert maximum softening and solvent action. The solvents include a mixture of benzene and aliphatic alcohols or cyclic aliphatic oxides, such as tetramethylene oxide. An aliphatic acid ester, such as ethyl acetate in acetone can also be added. The benzene may be replaced by a mixture of halogenated aliphatic hydrocarbons.
U.S. Pat. No. 3,179,609 describes compositions useful for removing coatings and finishes such as paints, varnishes, lacquers, shellac, gums, and natural and synthetic resins which comprise (a) an active organic solvent, including binary, tertiary, etc., mixtures thereof, (b) a viscosity thickener comprising resinous polyethylene oxides), and (c) an evaporation retardant or film-forming compound. Numerous solvents (a) are disclosed including binary mixtures. Methylene chloride containing benzene, methanol, acetone, and the like are preferred.
U.S. Pat. No. 3,538,007 discloses a paint stripper comprising 54-77 parts of chlorinated liquid hydrocarbon solvent, 1-4 parts of carboxylic acid having 1-4 carbons, 1-6 parts of propargyl alcohol, 0-2 parts of non-ionic wetting agent, 0-15 parts of liquid aromatic hydrocarbon solvents, 0-6 parts of a coupling agent, 0-30 parts of phenol or alkyl substituted phenol, 0-2 parts of a thickener, and 0-2 parts of an evaporation retarder. The aromatic liquid hydrocarbon can be benzene, toluene, or xylene.
U.S. Pat. No. 3,574,123 describes a paint stripper comprising 50-90 parts of a chlorinated liquid hydrocarbon solvent, 2-15 parts of a lower aliphatic alcohol or glycol ethers, 0.1-15 parts of a lower carboxylic acid, 2-30 parts of hydroxybenzenes, 2-10 parts of a fatty acid sulfonate or a salt of a fatty amine carboxylic acid, and 0.1-10 parts of aqueous ammonium bifluoride. This composition can also contain inert organic aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, otho-ethyltoluene, di-ethylbenzene, and isopropyl benzene, the lower alkyl substituted benzenes boiling at 170.degree. F. and higher being preferred.
U.S. Pat. No. 3,592,691 describes the removal of photo resist mask residuals from a semiconductor substrate by immersing the substrate in a photoresist solvent and heating the solvent at 150-250.degree. C. and at a pressure of about 300 psig for a time period of 1/4-3 hours. The solvent composition comprises trichloroethylene, isopropanol, and xylene with up to a few percent of methylene chloride. The isopropanol may be replaced wholly or partially with lower boiling point aliphatic alcohols such as ethanol.
U.S. Pat. No. 3,743,542 describes a method for removing paint from metal surfaces by boiling a solvent or solvent mixture and contacting the painted metal surface with the vapors of the solvent mixture, preferably while refluxing the vapors in a closed system. It is especially useful for removing durable paints such as those based on vinyl, acrylic, or epoxy resins. The stripping composition comprises solvents and mixtures thereof including chlorinated liquid hydrocarbons, hydrogenated aromatic solvents, saturated heterocyclic compounds, surface active agents, imidazole derivatives, alkynyl alcohols, glycol ethers, carboxylic acids, ethanolated alkyl quanidine amine complexes, and aliphatic alcohols.
Examples of patents which disclose alternative solvents are mentioned below.
U.S. Re No. 27,432 is directed to a process for removing polymeric materials from processing equipment with tetrahydrofuran. It teaches that numerous solvents have been known for dissolving vinyl halides of various molecular weights including trimethylene oxide, tetramethyl urea, dimethyl acetamide, tetrahydrofuran, cyclohexanone, cyclopentanone, cyclohexene oxide, diethyl acetamide, methyl ethyl ketone, and dioxane.
U.S. Pat. No. 3,784,477 relates to removal of paints, varnishes, and similar finishes from wood and metal objects without damage to grain or glue joints. It teaches that xylene or aromatic naphthas can be used as an extender for solvents dimethylformamide or dimethyl acetamide, with little change in paint removal activity, and further that xylene can be diluted or extended freely with methyl alcohol up to about 20% of its weight.
It is also known to incorporate cyclic ethers, including trioxane, into cleaning and coating remover solvents.
For example, U.S. Pat. No. 3,723,331 discloses a method for stabilizing halogenated solvents derived from aliphatic saturated hydrocarbons. Stabilization is accomplished by incorporating therein trioxane associated with an aliphatic alcohol, particularly tertiary butanol and/or an epoxide which is liquid at ordinary temperature, particularly butylene oxide. The compositions are used as solvents for grease removal and/or for cleaning of metal parts or components. British Patent No. 2,024,243 discloses a similar composition for stabilizing 1,1,1-trichloroethane in which tertiary butyl alcohol, trioxane, an epoxide, a nitroalkane and an aliphatic or cyclic amine are added.
U.S. Pat. No. 3,904,430 describes a method of cleaning a contaminated article in a system which comprises using a solvent mixture comprising a halogenated hydrocarbon solvent and an auxiliary solvent which does not form a azeotrope with the halogenated hydrocarbon solvent wherein the article is contacted with a first heated liquid mixture of the solvents and the article rinsed with a second liquid mixture containing a lower proportion of the auxiliary solvent. Auxiliary solvents which are disclosed include alcohols and cyclic ethers of which 1,4-dioxane is specifically disclosed.
German Offenlegungsschrift No. 2,118,870 discloses a paint remover and solvent for varnishes and paints comprising an acetal of diol such as 1,3-dioxolane and 5 to 60 parts, preferably 10 to 40 parts, based 100 parts of the cyclic acetal or acetal blend of trioxane. The addition of trioxane results in the retention of the volatile solvents that are effective during the paint removal. Specific examples using trioxane include 1,3-dioxolane/trioxane in a 4:1 mixing ratio, and butane diol-1,4-formal/trioxane in a 7:3 mixing ratio.
German Offenlegungsschrift No. 2,123,563 discloses a paint remover, solvent, and the like based on organic solvents containing 5 to 60 and preferably 10 to 50 parts by weight of trioxane based on 100 parts per weight of the mixture as a retention agent. Specific examples include trioxane mixed with each of chlorinated hydrocarbons, xylene, ethyl acetate, methyl ethyl ketone and acetone.
In application U.S. Ser. No. 205,143, filed June 10, 1988, now U.S. Pat. No. 9,830,772, the inventor discloses a coating stripper composition based on trioxane. The composition preferably contains equal amounts of trioxane and co-solvents of an aliphatic alcohol such as methanol and an aromatic hydrocarbon such as xylene.
While stripper compositions containing benzene, xylene, toluene, methylene chloride, and mixtures thereof have enjoyed commercial success, these solvents have important disadvantages. For example, these solvents are not readily biodegradable, are toxic and harmful to human skin, and are highly volatile, thus, dispersing into the atmosphere and rendering the stripper composition less useful due to evaporation from the coating surface. In general, these solvents are harmful to both the extended environment including soil, air, ground water and the localized environment where the solvents are being used and where the user must take substantial care to avoid skin contact and excessive inhalation of solvent vapor.
Unfortunately, many surfaces having coatings that need to be removed are located out of doors, such as homes made of wood or painted brick, commercial buildings, and industrial structures which are, exemplified by steel monuments, distillation columns, steel bridges, paper mills, steel ships, and the like. After application of the stripper, the lifted coating must also be physically removed from the surface before it can be painted again. Removing methylene-stripped coatings from such surfaces may require use of ladders and suspended platforms and arms-length work on the lifted coatings, and, thus, can be harmful and even dangerous to workmen. Moreover, the use of conventional stripper solvents presents major environmental hazards, when employed on a large scale, because such solvents are highly volatile and are not readily biodegradable.
There is consequently a need for a stripper composition which has reduced levels of toxic solvents, which, for example, is water borne, readily biodegradable, and effective. There is also a need for a stripper which can be removed by use of water and particularly by use of a jet or stream of water which can be applied to the stripped surface from a distance.